Shaft-type electric furnace

Abstract

To provide a shaft type electric furnace equipped with a water-cooling mechanism in which water leakage hardly occurs and which can lengthen a service life of a preheating shaft.SOLUTION: A shaft type electric furnace in which a cold iron source is supplied to a furnace body through a preheating shaft includes a water-cooling box 10 disposed on an inner wall face 3Ab side of the preheating shaft. The water-cooling box 10 includes a wall plate part 11A that faces the inner wall face 3Ab of the preheating shaft and can come into contact with the cold iron source charged into the preheating shaft, a bottom plate part 11D being continuous to the lower end of the wall plate part 11A, and a water jetting section 12 that sprays water to the inner face of the wall plate part 11A, where at least the lower part of the wall plate part 11A and at least a part on the wall plate part side of the bottom plate part 11D are composed of one plate member 11F.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a shaft-type electric furnace.

Background Art

[0002] A shaft-type electric furnace is a furnace in which a cold iron source such as scrap is supplied to a furnace body (electric furnace) through a preheating shaft, and the supplied cold iron source is melted into molten steel. The cold iron source supplied to the preheating shaft is preheated by using the sensible heat of exhaust gas in the preheating shaft. Therefore, the shaft-type electric furnace is an electric furnace with high energy efficiency.

[0003] For example, Patent Document 1 discloses an electric furnace (melting furnace) having a preheating shaft as a shaft-type electric furnace. In the shaft-type electric furnace described in Patent Document 1, high-temperature exhaust gas generated during the melting process is discharged through the preheating shaft. At this time, by supplying a cold iron source such as scrap to be melted to the melting chamber through the preheating shaft, the cold iron source in the preheating shaft can be preheated by the exhaust gas.

[0004] Also, conventionally, in order to protect the housing frame of the preheating shaft through which high-temperature exhaust gas passes, a tube cooler (water cooling mechanism) may be provided at the lower part of the preheating shaft that is most heated by the exhaust gas. The tube cooler is generally cooled by supplying cooling water to a tube arranged along the inner surface surrounding the four sides of the housing frame.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] While tube coolers offer excellent cooling efficiency, the circular cross-sectional shape of the tubes makes it difficult to control their wall thickness. Furthermore, if the tube wall thickness becomes too thin, the tubes are more prone to cracking due to contact with the cold iron source, raising concerns about water leakage.

[0007] Furthermore, in a tube cooler, the water pressure of the cooling water flowing inside the tubes is high to enhance cooling capacity. If a water leak occurs, a large amount of water will leak out and blow onto the cold iron source that is being preheated.

[0008] Furthermore, because the tubes of the tube cooler have a circular cross-section, they are difficult to repair by welding if their wall thickness thins or cracks develop over time. In addition, an increase in the number of repairs to the tube cooler shortens the service life of the preheating shaft itself, which may result in prolonged production stoppages for shaft-type electric furnaces.

[0009] This invention was made in view of the above-mentioned problems, and aims to provide a shaft-type electric furnace equipped with a water-cooling mechanism that is less prone to water leakage and can extend the service life of the preheating shaft. [Means for solving the problem]

[0010] To solve the problem, according to one aspect of the present invention, a shaft-type electric furnace is provided in which a cold iron source is supplied to the furnace body through a preheating shaft, and the preheating shaft has a water-cooling box disposed on the inner wall side, the water-cooling box comprising a wall plate portion facing the inner wall surface of the preheating shaft and capable of contacting the cold iron source loaded into the preheating shaft, a bottom plate portion continuous with the lower end of the wall plate portion, and a water injection portion that sprays water onto the surface of the wall plate portion facing the inner wall surface of the preheating shaft, the gist of which is that at least the lower part of the wall plate portion and at least the portion of the bottom plate portion on the wall plate portion side are made of a single plate material. [Effects of the Invention]

[0011] According to an aspect of the present invention, cooling water is sprayed onto the inner surface of the wall plate portion that can come into contact with the cold iron source, thereby cooling the wall plate portion that is heated by the exhaust gas passing through the preheating shaft. Therefore, unlike a tube cooler, the water-cooled box can prevent the internal pressure inside the water-cooled box from becoming too high. Consequently, the wall plate portion of the water-cooled box is less likely to crack due to collision with the cold iron source compared to a tube cooler. Furthermore, even if a crack occurs in the wall plate portion, since the internal pressure inside the water-cooled box is not high, even if water leakage occurs, it is prevented from flowing out into the preheating shaft by simply squirting out from the crack.

[0012] Furthermore, by constructing the joint between the wall plate and the bottom plate on the cold iron source side within the preheating shaft with a single plate, the stress on the joint is reduced, making water leakage from the joint less likely.

[0013] Here, the joint between the wall panel and the bottom panel is a stress concentration point. If the wall panel and bottom panel are joined at this joint by fillet welding, the welded joint becomes prone to cracking due to the temperature history load that occurs over time. In contrast, according to the embodiment of the present invention, there is no weld at the stress concentration point of the joint, and therefore the strength of the water cooling box structure over time is improved accordingly.

[0014] As a result, according to an aspect of the present invention, it is possible to provide a shaft-type electric furnace equipped with a water-cooling mechanism that is less prone to water leakage and can extend the service life of the preheating shaft. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows an example of a partially fractured shaft-type electric furnace according to an embodiment of the present invention. [Figure 2] This is a cross-sectional view showing an example of the placement of a water cooling box on the preheating shaft. [Figure 3] This is a vertical cross-sectional view illustrating a water cooling box. [Figure 4] This is a longitudinal cross-section showing another example of a water cooling box.

Embodiments for Carrying Out the Invention

[0016] Next, embodiments of the present invention will be described while referring to the drawings. (Configuration) [[ID=]](10) The shaft-type electric furnace 1 of the present embodiment includes a furnace body 2 and a preheating shaft 3 as shown in FIG. 1. The furnace body 2 is, for example, an electric furnace, and melts a cold iron source 4 such as supplied scrap into molten steel 5. The preheating shaft 3 is a chimney-shaped shaft extending upward, with its lower part connected to the furnace body 2 and forming a guide path S for supplying the cold iron source 4 toward the furnace body 2.

[0017] In FIG. 1, the symbol R indicates an example of the flow of exhaust gas from the path body. The exhaust gas R passes through the preheating shaft 3 and is further discharged to the outside through a dust collection duct provided at the upper part of the preheating shaft 3.

[0018] As shown in FIG. 2, in the shaft-type electric furnace 1 of the present embodiment, a plurality of water-cooled boxes 10 are arranged on the inner wall surface 3Ab side (guide path S side) of the housing frame 3A of the preheating shaft 3. The symbol 3Ab is the outer wall surface of the housing frame 3A.

[0019] The plurality of water-cooled boxes 10 are arranged in the circumferential direction along the inner wall surface 3Ab of the preheating shaft 3. Also, the plurality of water-cooled boxes 10 are arranged in a stacked state in the vertical direction along the inner wall surface of the preheating shaft 3 (see FIG. 3). Note that there may be a gap between the water-cooled box 10 and the inner wall surface 3Ab of the housing frame 3A.

[0020] As shown in FIG. 3, the water-cooled box 10 includes a box-shaped housing 11 and a water injection part 12 arranged inside the housing 11.

[0021] The housing 11 includes a wall plate part 11A facing the guide path S side, a wall plate part 11B located on the inner wall surface 3Ab side of the housing frame 3A of the preheating shaft 3, a pair of side wall parts facing each other in the width direction (the direction perpendicular to the paper surface in FIG. 3), a top plate part 11C, and a bottom plate part 11D, and forms a box-shaped closed space inside.

[0022] In this specification, the wall plate portion 11A facing the guide path S side is also referred to as the cooling side wall plate portion 11A. The cooling side wall plate portion 11A is made of, for example, a flat panel material. The outer surface of the cooling side wall plate portion 11A does not have to be flat. A bead extending along the vertical direction or the like may be provided to increase the surface area (cooling capacity). Note that the wall plate portion 11B, the top plate portion 11C, etc. located on the inner wall surface 3Ab side of the housing frame 3A of the preheating shaft 3 are not particularly limited in shape.

[0023] The outer surface of the cooling side wall plate portion 11A constitutes a surface that can contact the exhaust gas R discharged from the furnace body 2 and the cold iron source 4 passing through the guide path S.

[0024] The water injection portion 12 is a device that sprays water onto the inner surface of the cooling side wall plate portion 11A to cool the cooling side wall plate portion 11A. The water injection portion 12 of the present embodiment includes a header 12A extending vertically and a plurality of injection nozzles 12B. The injection nozzles 12B are provided on the header 12A and spray cooling water toward the inner surface of the cooling side wall plate portion 11A. And cooling water can be pumped to each nozzle 12B through the header 12A. A plurality of sets of the water injection portion 12 with such headers 12A with nozzles 12B are arranged over a pair of side wall portions facing each other in the width direction of the housing 11 (the direction perpendicular to the paper surface in FIG. 3).

[0025] In the water-cooled box 10 of the present embodiment, at least the lower part of the cooling side wall plate portion 11A and the portion of the cooling side wall plate portion 11A of at least the bottom plate portion 11D are formed of a single plate material 11F. That plate material 11F is also referred to as a connecting plate 11F.

[0026] The connecting plate 11F has an L shape (angle shape) and includes a rising portion 11Fa extending vertically, a horizontal portion 11Fc extending horizontally, and an arc-shaped bent portion 11Fb connecting the rising portion 11Fa and the horizontal portion 11Fc. The angle formed by the rising portion 11Fa and the horizontal portion 11Fc does not have to be 90 degrees. The connecting plate 11F may be formed, for example, by bending a plate material to form the bent portion 11Fb.

[0027] From the viewpoint of stress relaxation, the radius of curvature of the arc shape of the curved portion 11Fb is preferably 20 mm or more.

[0028] In the example shown in Figure 3, the cooling side wall plate section 11A is composed of vertical plates 11E made of vertically extending plate material and a rising portion 11Fa of the connecting plate 11F. In this example, the lower end of the vertical plate 11E and the upper end of the rising portion 11F are joined by butt welding. Reference numeral D2 indicates the location of the butt weld. The joining of the lower end of the vertical plate 11E and the upper end of the rising portion 11F may be done by means other than welding, such as bolting.

[0029] Here, the vertical plate 11E and the connecting plate 11F may be made of a single plate material. In this case, the lower part of the plate material can be bent to form the curved portion 11Fb described above. As shown in Figure 3, when the cooling side wall plate portion 11A is made of the vertical plate 11E and the rising portion 11Fa of the connecting plate 11F, the dimensions of the plate material to be bent (connecting plate 11F) become smaller, making it easier to process. However, welding at the reference numeral D2 is required.

[0030] In the example shown in Figure 3, the bottom plate 11D is composed of a horizontal plate 11G extending laterally and a horizontal portion 11Fc of the connecting plate 11F. The horizontal plate 11G and the horizontal portion 11Fc of the connecting plate 11F are joined by butt welding at the position indicated by the numeral D1. The horizontal board 11G and the connecting board 11F may be made from a single piece of wood.

[0031] Here, the curved portion 11Fb constitutes the joint between the cooling side wall plate portion 11A and the bottom plate portion 11D. For this reason, the curved portion 11Fb is also referred to as the joint.

[0032] Furthermore, the water cooling box 10 of this embodiment has a baffle plate 13 that prevents the cooling water sprayed from the water injection unit 12 from directly hitting the curved section 11Fb. In the example shown in Figure 3, the baffle plate 13 is positioned below the lowest nozzle 12B and above the curved portion 11Fb, protruding diagonally downward from the inner surface of the cooling side wall plate 11A. The shape of the baffle plate 13 does not need to be a flat plate, and the tip of the baffle plate 13 may be close to or in contact with the bottom plate 11D.

[0033] Furthermore, rubber material or other cushioning material may be placed on the inner surface of the curved portion 11Fb to prevent the cooling water from directly contacting the curved portion 11Fb. In Figure 3, reference numeral 14 denotes a drain pipe, which is a pipe for draining water that has fallen onto the bottom plate portion 11D to the outside.

[0034] (Operation and other functions) The cold iron source 4 supplied to the furnace body 2 through the guide passage S in the preheating shaft 3 is preheated by the exhaust gas R flowing from bottom to top in the preheating shaft 3.

[0035] In this case, by placing the water-cooled box 10 on the inner surface side of the preheating shaft 3 through which the exhaust gas R passes, the heating of the main frame 3A of the preheating shaft 3 by the exhaust gas R is suppressed, thereby improving the lifespan of the preheating shaft 3.

[0036] In this embodiment of the water-cooled box 10, cooling water is sprayed onto the inner surface of the cooling side wall plate 11A that comes into contact with the cold iron source 4 and exhaust gas R to cool the cooling side wall plate 11A. As a result, unlike a tube cooler, this embodiment of the water-cooled box 10 prevents the internal pressure inside the water-cooled box 10 from becoming too high, making it less likely for cracks to occur in the cooling side wall plate 11A due to collision with the cold iron source 4 compared to a tube cooler.

[0037] Furthermore, even if a crack occurs in the cooling side wall plate 11A, the internal pressure inside the water cooling box 10 is not high, so it is possible to prevent water from gushing out from the crack towards the guide passage S, and the impact on the preheated cold iron source 4 passing through the preheating shaft 3 can be reduced compared to a tube cooler.

[0038] Furthermore, in this embodiment, the curved portion 11Fb, which is the joint between the cooling side wall plate portion 11A and the bottom plate portion 11D on the cold iron source 4 side located within the preheating shaft 3, is constructed from a single plate material. This reduces the stress on the curved portion 11Fb and makes it less likely for water to leak from the curved portion 11Fb.

[0039] Here, the joint (bent portion 11Fb) between the cooling side wall plate 11A and the bottom plate 11D becomes a stress concentration point. If the plate material constituting the cooling side wall plate 11A and the plate material constituting the bottom plate 11D were joined at this joint location by fillet welding, cracks would easily occur in the welded joint due to the temperature history load that develops over time.

[0040] In contrast, in this embodiment, there is no weld at the joint location, which is a stress concentration point, and therefore the strength against temperature history over time at the joint is improved. Furthermore, by making the joint a circular arc shape in cross-section, stress concentration at the joint can be further reduced.

[0041] As a result, in this embodiment, water leakage from the body 11 of the water-cooling box 10 is less likely to occur, and therefore, a shaft-type electric furnace 1 equipped with a water-cooling mechanism can be provided that extends the service life of the preheating shaft 3.

[0042] Furthermore, in this embodiment, the baffle plate 13 prevents the cooling water from directly hitting the bent portion 11Fb, thereby easing the stress on the bent portion 11Fb, which is the joint, and further extending the lifespan of the water cooling box 10. When the bent portion 11Fb is spray-cooled, high stress is generated at the bent portion 11Fb. This is prevented by the baffle plate 13.

[0043] (modified version) Figure 4 shows a modified example of the water cooling box 10 of this embodiment.

[0044] In the water-cooled box 10 shown in Figure 4, the bottom plate portion 11D is inclined such that the side of the preheating shaft 3 on the frame 3A side is lower than the side of the joint portion 11Fb. That is, the bottom plate portion 11D is inclined downwards as it moves away from the cooling side wall plate portion 11A, that is, as it approaches the inner wall surface of the preheating shaft 3. There are no particular restrictions on the inclination angle, but for example, it has a downward angle of 5 degrees or more and 45 degrees or less with respect to the horizontal.

[0045] As shown in Figure 4, when the bottom plate 11D is tilted, water that falls onto the bottom plate 11D is more likely to flow towards the drain pipe 14. Furthermore, since the bending angle of the curved section 11Fb is smaller compared to the case in Figure 3, it helps to alleviate stress concentration in the curved section 11Fb.

[0046] (others) This disclosure may also take the following form: (1) A shaft-type electric furnace in which a cold iron source is supplied to the furnace body through a preheating shaft, The preheating shaft has a water-cooling box positioned on the inner wall side, The water cooling box comprises a wall plate portion facing the inner wall surface of the preheating shaft and capable of contacting the cold iron source loaded into the preheating shaft, a bottom plate portion continuous with the lower end of the wall plate portion, and a water spray portion that sprays water onto the wall plate portion facing the inner wall surface of the preheating shaft. At least the lower part of the wall panel and at least the portion of the base plate that faces the wall panel are made from a single board. (2) The above-mentioned board material is curved in an arc shape at the joint between the wall board portion and the bottom board portion, The bottom plate portion is formed by butt-welding the end of one of the above-mentioned plates to the bottom plate portion side of another plate. (3) The device has a baffle plate to prevent the cooling water sprayed from the water injection unit from directly hitting the joint between the wall plate and the bottom plate. (4) The bottom plate is inclined such that the inner wall surface of the preheating shaft is lower than the wall plate side. [Examples]

[0047] For the water-cooled box 10 with the shape shown in Figure 3, as described in this embodiment, a heat transfer and thermal stress analysis (FEM analysis) was performed using CAE to determine the stress applied to the curved section 11Fb. MSC.Marc was used as the analysis software to perform the analysis.

[0048] At this time, the internal shape of the joint (bent section 11Fb) was changed, and the stress generated in the bent section 11Fb was determined. In addition, the analysis was performed with two different plate thicknesses for the cooling side wall plate section 11A: 50 mm and 32 mm.

[0049] The results are shown in Table 1. [Table 1]

[0050] Here, the "Shape of the curved section" column in Table 1 represents the shape of the inner surface of the curved section 11Fb. "Right angle" refers to the case where the inner surface of the curved section 11Fb is a right angle. "Filler fillet leg length 16mm" refers to the shape where a 16mm leg length of filler is added to that right angle. "R20" refers to the case where the inner surface of the curved section 11Fb is an arc shape with a radius of curvature of 20mm. "Right angle" simulates a case where the cooling side wall plate 11A and the bottom plate 11D are fillet welded at the curved section 11Fb, and "fillet leg length 16mm" simulates a case where the thickness is increased by building up material on the inside of the fillet weld. Furthermore, "R20" simulates a case where the curved section 11Fb is made from a single plate material that is curved in an arc shape.

[0051] Furthermore, in the heat transfer analysis, the calculation was performed under the condition that the initial temperature was 30°C and the temperature was raised by receiving radiant heat from a heat source of 1300°C for 10 hours. The analysis was also performed using elastoplastic calculations.

[0052] As can be seen from Table 1, it was found that when the joint between the cooling side wall plate 11A and the bottom plate 11D is constructed by welding, bending a single plate material to form the bent portion 11Fb (joint) reduces stress and makes it less likely for cracks to occur at the joint.

[0053] Furthermore, heat transfer and thermal stress analysis confirmed that higher stress concentrations occur in the curved section 11Fb compared to the flat cooling sidewall section 11A.

[0054] Furthermore, it was found that the thinner the thickness of the cooling side wall plate 11A, the smaller the stress at the bent portion 11Fb. However, since the cooling side wall plate 11A is in contact with the cold iron source 4 such as scrap, durability (strength) to withstand the contact of the cold iron source 4 is necessary. Therefore, the thickness of the cooling side wall plate 11A should be set appropriately considering the required durability (strength). [Explanation of symbols]

[0055] 1. Shaft-type electric furnace 2 Furnace body 3 Preheating shaft 3A Structural Frame 3Ab Inner wall surface 4 cold iron source 5 Molten steel 10 Water Cooling Boxes 11 Body 11A Cooling side wall plate section 11D Bottom plate part 11E Vertical plate (cooling side wall plate) 11F connecting plate (plate material) 11Fa rising part (cooling side wall plate part) 11Fb Curved section (joint) 11Fc Horizontal part (bottom plate part) 11G Horizontal plate (bottom plate) 12 Water injection part 12A Header 12B Spray Nozzle 13 Obstacle board 14 Drain pipe R Exhaust gas (flow) S Guideway

Claims

1. In a shaft-type electric furnace, the cold iron source is supplied to the furnace body through a preheating shaft, The preheating shaft has a water-cooling box positioned on the inner wall side, The water cooling box comprises a wall plate portion facing the inner wall surface of the preheating shaft and capable of contacting the cold iron source loaded into the preheating shaft, a bottom plate portion continuous with the lower end of the wall plate portion, and a water spray portion that sprays water onto the surface of the wall plate portion facing the inner wall surface of the preheating shaft. At least the lower part of the wall panel and at least the portion of the base plate that faces the wall panel are made of a single board. The above-mentioned board material is curved into an arc shape at the joint between the wall panel and the bottom panel. The end of one of the above-mentioned plates is butted and welded to the bottom plate side of another plate to form the bottom plate. A shaft-type electric furnace characterized by the following features.

2. The device has a baffle plate to prevent the cooling water sprayed from the water injection unit from directly hitting the joint between the wall plate and the bottom plate. The shaft-type electric furnace as described in feature 1.

3. The bottom plate is inclined such that the inner wall surface of the preheating shaft is lower than the wall plate side. A shaft-type electric furnace as described in 1 or 2, characterized by the above.

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